1. Field of the Invention
The present invention relates generally to trains traversing a complex track network and the braking arrangements and systems of these trains, and in particular trains with a pneumatically-controlled braking arrangement having a controller for adjusting the air pressure of air transmitted through a brake pipe from a lead locomotive to a rear railcar in a train consist.
2. Description of the Related Art
In the railroad industry, multiple trains are traversing a complex track network during normal operations, which requires accurate and effective communication and control to ensure efficiency and safety. In order to provide control to the operator (or automated control features), trains are equipped with a braking arrangement and system that permits the safe control and braking of the train, normally through the use of a braking arrangement that is operatively connected to one or more railcars in the train consist.
In one particular embodiment, a train is equipped with a pneumatically-controlled braking arrangement, which includes a controller for adjusting air pressure of air transmitted through a brake pipe from a lead locomotive to a rear railcar. Normally, this operation is effected through the use of a brake valve (and/or brake cylinder) positioned on each railcar. In operation, the air pressure is communicated from the lead locomotive (or brake controller) through the brake pipe and each valve, such that appropriate and uniform braking occurs.
However, in order to ensure uniform and consistent braking between the railcars, the propagation time for air to travel from the lead locomotive to the end-of-train (or rear railcar) through the brake pipe should be determined. In particular, this air propagation rate is used to determine the braking performance of the train, since variations in the air propagation rate impact brake setup time at each railcar in the train (and, thus, the overall train braking performance). Further, knowing the actual air propagation rate through the train would allow for an accurate prediction of the setup times and braking force, and ultimately provides less uncertainty in stopping distance predictions.
In a typical train, a brake pipe reduction of 15 pounds per square inch (psi) propagates to the rear at a rate of approximately 350 feet per second (ft/sec). Presently, the propagation rate through the train is a constant that is chosen at a conservative value to account for extremes in temperature, pressure, humidity, and the physical configuration of each railcar. Predictive braking algorithms, such as those used in train control systems, benefit from eliminating all conservative constants, and replacing them with known, verifiable values. Accurately determining propagation rate (or delay) can lead to significant improvements in predictive braking processes.
Under normal operating conditions, the brake pipe is modulated only from the front of the train to the rear of the train via the air brake control system. Reducing the pressure in the brake pipe is a signal to the brake valves on each car for controlling braking force at each railcar. Greater levels of pressure reduction in the brake pipe indicate a call for greater braking force on each rail car through the air brake valve and brake cylinder located at each railcar. Reducing the brake pipe pressure at a “service” rate indicates that the brake valve on each railcar is to operate in a normal “service” mode. However, if the brake pipe pressure reduction exceeds the service rate, the brake valve on each car operates in the “emergency” mode, where the arrangement not only creates a braking force on the railcar where it is located, but also vents the brake pipe locally to aid in propagation of the brake pipe reduction.
Undesired emergency brake applications can occur if a brake valve enters emergency mode without an intentional trigger through the brake pipe. When an undesired emergency brake application occurs, the entire train enters the emergency braking state as the signal propagates through the brake pipe to both the front end and rear end of the train from the device that first triggered the emergency. Therefore, it is beneficial if a defective brake valve can be identified to eliminate any such “faulty” brake applications.
Various systems and arrangements have been provided to address certain deficiencies and issues that arise from the use of pneumatically-controlled braking arrangements. See, e.g., U.S. Publication Nos.: 2005/0240322 to Peltz et al.; and 2006/0290199 to Beck et al.; and U.S. Pat. Nos. 4,066,299 to Clements; 4,582,280 to Nichols et al.; 5,963,883 to Cunkelman et al.; 6,375,276 to Delaruelle; and 6,619,138 to Kettle, Jr. et al. However, there is still considerable room in the art for systems and methods for enhancing the operation of existing braking arrangements and train operations.